This invention pertains to a process for the production of tertiary butyl esters. More specifically, this invention pertains to a continuous process for the preparation of tertiary butyl esters through the reaction of a ketene with tertiary butyl alcohol containing a finite amount of water.
Carboxylic acid esters of tertiary butyl alcohol are useful for the production of agrochemicals, coatings, dyes, and solvents. There are several documented methods for the production of tertiary butyl esters. One well-known method for the preparation of tertiary butyl acetate (t-butyl acetate) is by the reaction of isobutylene with acetic acid in the presence of a variety of catalysts. Some of the many types of catalysts used for this reaction include metal silicates, cation exchange resins, acidic ion-exchange resins, sulfuric or other protic acids, as well as modified copolymers of styrene and divinylbenzene.
U.S. Pat. No. 5,866,714 describes a method for producing tertiary butyl acetate by the reaction of isobutylene with acetic acid using byproduct tertiary butyl alcohol to suppress olefin polymerization.
U.S. Pat. No. 4,360,406 describes a method for producing tertiary butyl alcohol and tertiary butyl acetate by the reaction of isobutylene with an aqueous solution of an aliphatic carboxylic acid in the presence of an acidic ion-exchange resin. In this process the t-butyl acetate is produced as a minor impurity, which is removed from the process by azeotropic distillation with water.
U.S. Pat. No. 4,009,203 describes a process for producing esters, including t-butyl acetate, by the reaction of an olefin with a halogenated aliphatic, halogenated aromatic or alkenic carboxylic acid in the presence of pre-formed acyloxystannic trihalide.
U.S. Pat. No. 3,102,905 describes a process for producing t-butyl acetate by the reaction of isobutylene and acetic acid in the presence of an organic sulfonic acid in the liquid phase. The crude product is then purified by means of distillation to give t-butyl acetate free of isobutylene.
U.S. Pat. No. 3,096,365 describes a process for producing tertiary esters from olefins and carboxylic acids in the presence of a polyvalent metal silicate catalyst. In this process a tertiary olefin is contacted with a carboxylic acid, in the presence of the catalyst, at temperatures not exceeding 300xc2x0 F. to yield the corresponding tertiary ester.
U.S. Pat. No. 3,072,714 describes a process for separating esters from a mixture comprising the said ester, sulfuric acid, and an alkanoic acid. The ester is produced from the sulfuric acid catalyzed reaction of the alkanoic acid with an olefin. The ester is recovered by phase separation after treating the crude reaction mixture with an aqueous alkaline solution.
U.S. Pat. No. 3,055,934 describes a method for producing tertiary esters from tertiary olefins in the presence of sulfuric acid. In this process a tertiary olefin is condensed with an aliphatic hydrocarbylmonocarboxylic acid in the presence of sulfuric acid to produce the corresponding tertiary alkyl ester. The crude tertiary ester is recovered by phase separation after extraction with water.
U.S. Pat. No. 3,053,887 describes a method of producing a t-butyl ester from the reaction of an alkanoic acid with isobutylene in the presence of a catalyst. In this process isobutylene is reacted with a lower alkanoic acid in the presence of a sulfonated copolymer of styrene and a cross-linking compound consisting of divinylbenzene at a temperature below 5xc2x0 C.
U.S. Pat. No. 3,031,495 describes a process for producing t-butyl acetate by the reaction of acetic acid with a tertiary olefin in the presence of a catalyst. In this process the acetic acid is contacted with the tertiary olefin at a temperature of 0-60xc2x0 C. and in the presence of a catalyst consisting of a divinylbenzene cross-linked polystyrene sulfonic acid cationic exchange resin containing water.
In the related art described above, isobutylene (or other tertiary olefins) is reacted with acetic acid (or other carboxylic acids) in the presence of strongly acidic catalysts to yield t-butyl acetate (or other tertiary esters).
Another known method for producing esters is by the reaction of acetic acid with alcohols. The reaction of acetic acid with many primary and secondary alcohols proceeds readily, without catalyst, to yield the corresponding ester and water (byproduct). The reaction of tertiary alcohols with acetic acid, however, does not proceed at useful rates without the use of a strong acid catalyst. With t-butyl alcohol, the reaction of acetic acid proceeds smoothly with a variety of strong acid catalysts but yields are often low due to the formation of unwanted by-products, especially isobutylene. When tertiary butyl alcohol is reacted with acetic acid in the presence of strongly acidic catalysts, a large amount of isobutylene gas is formed from the acid-catalyzed dehydration of tertiary butyl alcohol. Due to the formation of the isobutylene, this process requires special equipment that allows for the recovery of the isobutylene off-gas in a safe manner and results in reduced yields.
The production of t-butyl acetate from acetic acid and tertiary butyl alcohol is described in several patents. U.S. Pat. No. 5,151,547 discloses a process for producing an organic carboxylic acid ester from an organic carboxylic acid and an alcohol in the presence of a catalytic amount of sulfuric acid in the gas phase. As described above, when tertiary butyl alcohol is reacted with acetic acid in the presence of a variety of acid catalysts, isobutylene gas was a major by-product. The separation of the by-product gas from the corresponding ester requires special equipment to allow for the recovery of the gas in a safe manner.
U.S. Pat. No. 3,590,073 discloses a method of producing t-butyl acetate from the reaction of acetic acid and tertiary butyl alcohol in the presence of a sulfonic acid cation exchange resin. When this method of production of t-butyl acetate is employed, temperatures exceeding  greater than 40xc2x0 C. causes extensive decomposition of the product to isobutylene and acetic acid, which lowers yield dramatically.
German Patent Application No. 3,636,754 describes a continuous method of preparation of alkyl acetate from an alcohol and acetic acid in the presence of a mineral acid catalyst to yield the corresponding crude acetic acid ester. The crude ester is then purified by distillation.
In the related art described above, t-butyl acetate is produced by the reaction of a carboxylic acid with an alcohol in the presence of strong Lewis or mineral acid catalysts.
Another known method for the production of t-butyl acetate is by the reaction of acetic anhydride with tertiary butyl alcohol. This reaction proceeds without catalyst to yield t-butyl acetate and acetic acid. The major drawback of this method for producing t-butyl acetate is that for every mole of product produced, a mole of acetic acid by-product is also produced. A method for recovering the acetic acid must be developed to make the process economical. Another major drawback of this method for producing t-butyl acetate is that the reaction is somewhat sluggish, without the use of a catalyst, which restricts production rates. When a catalyst is used to improve the reaction rate, a variety of unwanted by-products are often produced making the production of pure t-butyl acetate more difficult without added purification equipment.
U.S. Pat. No. 3,489,796 describes a method for producing tertiary amyl acetate from acetic anhydride and tertiary amyl alcohol using hydrochloric acid as a catalyst. This method of producing tertiary amyl acetate gives product in good yield and high purity after fractional distillation.
In the related art discussed above, t-butyl acetate (or other tertiary esters) is produced by the reaction of acetic anhydride with tertiary butyl alcohol. The reaction between acetic anhydride and tertiary alcohols, including tertiary butyl alcohol, is somewhat sluggish and requires the use of an added catalyst to increase production rates. These catalysts often cause several unwanted by-products which makes the production of pure t-butyl acetate more difficult without added purification equipment.
Another known method for producing esters is by the direct reaction of an alcohol with a ketene. Ketene is an efficient acetylating agent toward many primary and secondary alcohols but it has been shown to be either non-reactive or very slow to react with tertiary alcohols, especially tertiary butyl alcohol, without the use of a catalyst. Strong acid catalysts, such as sulfuric acid or p-toluenesulfonic acid, are therefore commonly used to improve reaction rates (Hurd et al. J. Amer. Chem. Soc. 61 (1939) 3355-3359). Carboxylic acids also are known to catalyze the reaction between alcohols and dimethyl ketene (Satchell et al. J. Chem. Soc., B (1968), 889-897).
Rice et al. (J. Amer. Chem. Soc., 56 (1934), 1760), disclose the reaction of boiling tertiary butyl alcohol with ketene without added catalyst. Although under forcing conditions of temperature and concentration, the reaction was slow and incomplete and extensive polymerization of ketene was observed.
When an acid catalyst is used in the process for producing t-butyl acetate, the reaction proceeds more rapidly but often a large amount of isobutylene is observed as a byproduct from dehydration of the tertiary butyl alcohol. As stated before, a method for recovering the off-gas (isobutylene) would need to be implemented if t-butyl acetate is produced by this method on a large scale.
U.S. Pat. No. 2,018,759 describes a method of acetylation of liquid polyhydroxy aliphatic alcohols by means of a ketene. In this process a mixture of primary, secondary, and tertiary alcohols are treated with sufficient ketene to react with the primary alcohols. This mixture is then distilled, taking overhead the secondary and tertiary alcohols, and leaving the primary alcohol ester is the still bottom. The overhead mixture is then treated with ketene for a longer period of time, allowing for the reaction of the secondary alcohol with ketene to take place. In a similar operation as described above, the tertiary alcohol is distilled overhead leaving the secondary alcohol ester in the still bottom. This process is repeated until the tertiary alcohol is eventually converted to the tertiary acetate. This process requires mixtures of primary, secondary, and tertiary alcohols to be used in the process to produce primary, secondary, and eventually tertiary acetates after a long reaction time with the ketene. This process also requires several distillation and reaction steps.
U.S. Pat. No. 2,685,598 describes a method for preparing tertiary alcohol acetates by acetylating tertiary alcohols with ketene in the presence of a silica-alumina type catalyst. In this process ketene gas is contacted with a tertiary alcohol in the presence of the silica-alumina type catalyst. The products obtained from this reaction, which are mainly unreacted alcohol and the tertiary ester, are separated by means of distillation. The insoluble silica-alumina catalyst is then recovered by filtration.
U.S. Pat. No. 3,679,739 describes a method for producing esters of acetic acid by reacting ketene with alcohols in the presence of metal sulfides. In this process ketene gas is contacted with an alcohol and a mixture of the catalyst in a reactor apparatus. The mixture is stirred for a period of time, which can range from 30 minutes to 10 hours, and then the unreacted ketene is expelled from the mixture via a nitrogen purge. The ester product is then separated from the reaction mixture by means of distillation.
U.S. Pat. No. 5,840,962 describes a process for preparing an ester by the reaction of an alcohol with a ketene in an ester solvent in the presence of strong acid catalyst. In this process a mixture of alcohol and acid catalyst are continuously introduced into a reaction vessel in which ketene is also continuously introduced. The crude product is circulated to a refrigerator, or a second vessel, where excess ketene and a portion of the product (ester) are removed. Another portion of the product is re-circulated back to the reactor vessel for use as a solvent in the reaction. The acid catalyst used in this process is selected from a group consisting of sulfuric acid, toluenesulfonic acid, acetosulfuric acid, and other strong acids, and mixtures thereof. In the above-described processes, ketene and tertiary butyl alcohol are used as raw materials to produce t-butyl acetate, but all require strongly acidic catalysts to promote the reaction between the two.
The processes described above frequently rely on the use of strongly acidic homogeneous or hetergeneous catalysts to obtain reaction rates useful for commercial production of tertiary butyl esters. These catalysts often result in the production of by-products, such as isobutylene, which reduce yields and require additional expensive equipment to recover and purify the desired tertiary butyl ester. Thus, there is a need for an efficient and economical process for the production of tertiary butyl esters by the reaction of ketenes with tertiary butyl alcohol which is simple to operate and avoids the production of troublesome by-products.
We have discovered a novel, continuous process for producing tertiary butyl esters by the reaction of ketenes with tertiary butyl alcohol comprising:
I. continuously feeding a gaseous ketene and a liquid reaction composition comprising t-butyl alcohol containing a finite concentration of water to a reaction zone to provide a product comprising an ester of tertiary butyl alcohol; and
II. continuously removing said product from said reaction zone.
The present invention utilizes tertiary butyl alcohol containing a finite concentration of water as a starting material in an efficient, continuous process that provides tertiary butyl esters in high yield and assay. Without being bound by theory, the water present in the tertiary butyl alcohol reacts with the ketene to produce low concentrations of the corresponding carboxylic acid which may act as a catalyst for the esterification reaction but not as a catalyst for the production of by-products as observed with stronger mineral acids. In addition, the reaction of the ketene with carboxylic acids to form the corresponding anhydride maintains the concentration of carboxylic acid in the reaction mixture at a low but effective level which we believe further reduces the production of by-products. The present invention is especially useful for the preparation of tertiary butyl acetate by the reaction of ketene with tertiary butyl alcohol in a continuous process comprising:
I. continuously feeding gaseous ketene and a liquid reaction composition comprising t-butyl alcohol containing about 1 to 5 wt % water into an absorber reactor at a temperature of about 25 to 75xc2x0 C. to give a product comprising tertiary butyl acetate; and
II. continuously removing said product from said reaction zone.
Another preferred embodiment of the instant invention is a process for continuously recovering and refining the crude product of the absorber reactor by distillation to provide high purity tertiary butyl acetate and to separate unreacted tertiary butyl alcohol for recycle to the absorber reactor.